This invention relates to the field of carton constructions. More specifically, it relates to the field of carton constructions for manufacture from corrugated paper and in particular to corrugated carton constructions which employ an automatic bottom feature. By automatic bottom it is meant that when the carton is opened to its normal position for loading, the bottom is automatically deployed in position without the need for manually securing it. Such constructions in chipboard have long been known. Examplary of a large number of such prior art constructions are U.S. Pat. Nos. 2,781,160, 3,517,875, and 3,690,543. However, in corrugated constructions, particularly with large size containers, automatic bottom carton constructions have only recently come into use. An example of an automatic bottom carton construction is disclosed in pending U.S. Pat. application Ser. No. 523,996, now U.S. Pat. No. 3,960,313 assigned to the present assignee.
In the referenced patent application a corrugated carton construction is disclosed having an automatic bottom. That construction has a tendency, upon opening, to favor returning to the collapsed position until weight is placed on the bottom as occurs during the process of loading the carton.
A further problem occurs when it is desired to produce an overlapped bottom. That is, a bottom in which the panels overlap one another by a selected amount. This provides for increased strength and other desirable features. When an overlapped construction is utilized in corrugated automatic bottoms there is a tendency during opening for bridging to occur. Bridging is the phenomenon of two opposed sides, usually the longer two sides of a carton, to strike each other as they move towards the open position. Bridging prevents the cartons from fully deploying and requires that the carton be manually opened when this occurs.
It is accordingly an object of the present invention to provide an improved automatic bottom carton construction for corrugated container blanks.
It is another object of the present invention to provide a corrugated container blank with an automatic bottom feature which will not tend to collapse upon opening.
It is a further object of the invention to provide an automatic bottom corrugated carton blank which has an overlap and further including provisions for avoiding bridging of the bottom flap during opening of the carton.
Another object of the invention is to provide a corrugated carton construction employing pressure flaps on two of the bottom flaps whereby once a carton is opened to a point beyond the engagement of the pressure flaps with the adjacent flaps the carton is maintained in the opened position due to the presence of the pressure flaps preventing a return of the carton to its collapsed condition.
A further object of the invention is to provide a pressure and relief flap carton construction for a corrugated container wherein bridging is prevented due to the fact that opposite flap members are lowered to the deployed position in a specified order, one before the other.
Other objects and advantages of the invention will become apparent from the remaining portion of the specification.